John’s account of the Last Supper contains unique elements recorded nowhere else. John’s account, without noting any other details of the meal itself, states: “Now before the feast of the passover, when Jesus knew that his hour was come that he should depart out of this world unto the Father, having loved his own which were in the world, he loved them unto the end” (John 13:1). This verse establishes the emphasis of chapters 13–17, in which is found the loving service of Jesus, given with His coming sacrifice at Golgotha firmly in mind. The washing of the disciples’ feet, while no doubt connected with other higher ordinances, is used here as a paramount example of service. When Jesus teaches, “If I then, your Lord and Master, have washed your feet; ye also ought to wash one another’s feet” (John 13:14), the image of the greatest serving the least here is significant given the clearly stated divinity of the Johannine Jesus.
The discourses of chapters 13–17 that Jesus delivers to His disciples, both at the Last Supper and along the way to the garden that would be the scene of His arrest, are unique to the Gospel of John. Here Jesus taught His followers, both then and now, fundamental principles of love and service, all firmly focused on His own role as Savior and friend. Chapters 14 and 16 form a recognized doublet, in which Jesus teaches the necessity of His departing (see John 14:1–14; 16:4–7, 16–24), beginning with the well-known pronouncement, “In my Father’s house are many mansions: if it were not so, I would have told you. I go to prepare a place for you. And if I go and prepare a place for you, I will come again, and receive you unto myself; that where I am, there ye may be also” (John 14:2–3). In both chapters, Jesus balances the disciples’ sorrow at His departure with promises of the coming of a “helper” or “advocate” (paraklētos, King James Version “Comforter”; see John 14:15–26; 16:8–15) as well as with an assurance of the continuing peace and love of the Father that will remain with them (see John 14:27–31). Chiastically placed between the chapters is Jesus’s allegory of the vine: even when He is no longer physically present with them, they can nonetheless still abide in Him, drawing sustenance and life from Him as branches do from the main stem of a vine (see John 15:1–17).
All of these teachings focus squarely on Jesus. Even the five so-called Paraclete Sayings, which focus on the Holy Ghost as Comforter, or helper, identify His role not just as advocate but also as teacher, witness, prosecutor, and revealer (see John 14:15–18, 25–26; 15:26–27; 16:7–15). Jesus suggests that the Comforter is being sent to do these things for believers because Jesus Himself will soon be absent (see John 16:7).Indeed, the first of these sayings is actually about Jesus Himself and about the Holy Ghost only by comparison,since another Comforter by definition suggests a first Comforter:

If ye love me, keep my commandments.
And I will pray the Father, and he shall give you another Comforter, that he may abide with you for ever;
Even the Spirit of truth; whom the world cannot receive, because it seeth him not, neither knoweth him: but ye know him; for he dwelleth with you, and shall be in you.
I will not leave you comfortless: I will come to you. (John 14:15–18)

Remembering that the root meaning of paraklētos is “one who is called to someone’s aid,”the suggestion is that the Holy Ghost is an advocate or helper in the absence of Jesus. That yet another helper will come to our side, not just to advocate our cause in heaven before God (see D&C 45:3–5) but actually to come to us, is a point made clear by John 14:23 and Doctrine and Covenants 130:3. Furthermore, “comfortless” in John 14:18 is a translation of the Greek orphanous, literally “orphans,”suggesting that the Lamb of God will not leave believers fatherless—that is, devoid of comfort or the means of life—but that He, after His sacrificial death, will come and be a father to them through the gift of eternal life.
Eternal life—the kind of life that the Father and now Christ have—enjoyed in their presence is the subject of chapter 17, which is, in fact, a prayer rather than a discourse. Commonly known as the Intercessory Prayer, since in it Jesus prays that believers may be one with Him and the Father as He and the Father are one, it is also appropriately called “the Lord’s High-Priestly Prayer.”As the high priest under the Mosaic order represented the people before God, interceding for them before sacrificing, so here Jesus intercedes for His people before His own sacrificial death. While the word atonement (Greek katallagē) does not appear in this chapter, His prayer for the eternal union of disciples with Him and the Father represents the very essence of being at one with God. As He rose from that prayer, He went forth to perform the very Atonement that would make that unity possible.